The present invention relates to the field of targets, and in particular, a heat target for creating a thermal image composed of several bands and having at least one layer of electrically conducting material connected to two electrodes connected to means able to generate a potential difference between them, said layer being attached to a support.
Optronic devices for daytime and nighttime vision associated with weapons or weapon systems for land, sea, and air forces require a checking means for their validation. Targets enable the performance of these optronic devices to be quantified relative to contrasts in the visible or thermal infrared ranges, and relative to the detection, recognition, and identification ranges of systems at actual distances.
The STANAG 4347 and STANAG 4349 documents define procedures for optronic device testing. The former relates to the definition of normal static range performances of thermal imaging systems and the latter, to measuring the minimum resolvable temperature difference of thermal imaging systems.
The minimum resolvable temperature difference of thermal imaging systems is a function that, at an angular frequency, recognizes the smallest temperature detection .DELTA..theta. such that the target bars are placed:
normal to the axis of the observation system PA1 in the center of the field PA1 at a distance such that the successive bars, corresponding to a certain frequency, can be discerned by the optronic device tested. PA1 the objective PA1 the detector PA1 the electronics PA1 the display system PA1 the observer (normal visual acuity, good ability to evaluate colors, and good experience in this type of measurement) PA1 the atmospheric transmission. PA1 Nighttime Detection: PA1 Nighttime Recognition: PA1 Nighttime Identification: PA1 Daytime Detection: PA1 Daytime Recognition: PA1 Daytime Identification: PA1 vertical detection, PA1 horizontal detection, PA1 vertical recognition, PA1 horizontal recognition, PA1 vertical identification, PA1 horizontal identification.
The thermal imaging system links the thermal resolution and angular resolution of all the elements involved in the signal path within the system. Thus it depends on:
The function of the optronic is to supply visual information to the observer. The information has to be qualified and quantified.
For this purpose, the following three types of tests are generally performed: Detection, Recognition, and Identification.
Detection is the act of detecting a hot spot in a scene.
Recognition is finding out the type of object in a scene (tank, light vehicle, infantryman, etc.).
Identification is the precise determination of object (AMX30, T72, etc.).
For an object to be detected, recognized, or identified with some probability of success, the system must resolve a number of points on the object when placed at a far distance, and this number is a function of the type of test considered (Detection, Recognition, or Identification).
In fact, instead of points, spatial frequencies expressed in pairs of lines (or bars or bands) are considered.
There are empirical criteria that gives the probability of success probability value. The most widely used are the Johnson criteria.
The targets used for the visible mode correspond to the same spatial frequency as those of the thermal infrared mode.
Each type of test (Detection, Recognition, or Identification) and each mode (visible or thermal infrared) requires a specific target calculated by criteria relating to resolving power as a function of a 50% success probability.
In the thermal infrared mode, the targets used are the following:
uniform objective PA2 bar width: 2.30 m PA2 3.5 line pairs per objective PA2 bar width: 0.32 m PA2 7 line pairs per objective PA2 bar width: 0.16 m PA2 uniform objective PA2 bar width: 2.30 m PA2 3.5 line pairs per objective PA2 bar width: 0.32 m PA2 7 line pairs per objective PA2 bar width: 0.16 m
In the visible mode, the targets used are the following:
Since the pitch of the detector matrix may be different in the two directions (horizontal and vertical) the number of targets must be doubled to obtain both positions.
These types of targets are presented in FIGS. 1a to 1f.
In the visible mode, bands 5 are in one color shade and bands are in another shade of the same color, for example two shades of grey with a contrast of for example, 20%, contrast between black and white being considered at 100%.
In the infrared mode, the bands correspond to infrared radiation transmitting surfaces. Bands 5 correspond to a surface at a first temperature T1, and bands 6 correspond to a surface with a second temperature T2.
Targets 1a to If are used respectively for:
Thus, detection, recognition, and identification measures in the two modes, visible and thermal infrared, require 12 targets.
This multiplicity of targets has a number of disadvantages. Substantial logistics are required, and the time taken to change over the test type (detection, recognition, or identification), the position, (horizontal or vertical), and the mode (visible or infrared), require the target to be replaced each time, and considerably increasing the total testing time to evaluate the performance of an optronic device at an actual distance.
The goal of the invention is to overcome these disadvantages by providing a target that is very simple to manufacture, equally simple to maintain, and limits the time lost when the type of test is changed.